1. Field of the Invention
The present invention generally relates to a method of numerically controlled profile grinding, and more particularly to a method suited for grinding of cutter blades which are used in single-index milling of helical rotors.
2. Description of the Related Art
In forming a curved surface, i.e. profile, of a workpiece by a conventional numerical control method using a grinding wheel, it is so arranged that the grinding wheel approaches a target profile from a direction normal thereto. As shown in FIG. 6 illustrating the positional relationship between the target profile A-C-B and the grinding wheel 101, the position and attitude of the grinding wheel 101 are so controlled that a radial center line 104 of the grinding wheel 101 in a sectional plane containing the axis 102 of rotation of the grinding wheel 101 is constantly aligned with the normal 105 to the profile at a grinding point C. Hence, in this case, the object of control is the position or positional coordinates of a given point of the grinding wheel 101 and the inclination of its radial center line 104 represented by differential coefficient. For example, if the target profile is a two-dimensional curve in an orthogonal coordinate system, the position and attitude of the grinding wheel is controlled by means of three control variables, namely x-coordinate, y-coordinate and differential coefficient. The profile grinding method under control as described above, however, needs as one of the control variables the differential coefficient for attitude control besides the x- and y-coordinate for positional control, this resulting in a complicated mode of control and a shortened dressing interval as grinding is done by a given portion of the grinding wheel (a given point in the section) so as to cause local concentration of progress of abrasion.